Evaporative emission control systems are well known in internal combustion engine powered motor vehicles to prevent evaporative fuel, i.e., fuel vapor, from being emitted from the fuel tank into the atmosphere. These control systems typically include several primary components that control evaporative emission operations: vapor control valves, vapor management valves and a carbon canister for absorbing the vapors.
From time to time, fuel vapors may be vented improperly, resulting in reduced engine performance and the possibility of vapor emissions into the atmosphere. A variety of on-board diagnostic systems have been devised for detecting such emissions in the evaporative emission control system so that appropriate corrective measures may be taken.
Conventional emissions control may include: (1) an intake manifold of an engine connecting to a vapor control system in order to draw a vacuum on the control system, (2) sealing the vapor control system and/or, (3) bleeding-off and monitoring the resulting vacuum in the control system. With vehicles powered only by an internal combustion engine, these steps can only be performed while the engine is running. Coordinating the requirements of the engine control system and the evaporative emission control system test procedure places constraints on both systems. These problems are exacerbated in hybrid powered vehicles using both an internal combustion engine and an electric drive motor. Hybrid powered vehicles, when operating in an internal combustion (IC) mode, tend to run at relatively wide-open throttle for substantial periods in order to maximize operating efficiency. At open or near wide-open throttle, however, intake manifold pressure is lower, limiting the engine's ability to draw a vacuum in the evaporative emission control system to facilitate emissions detection.
Accordingly, a need exists in the art for a method of emissions detection that can be performed effectively while the engine is not running. The present invention is intended to satisfy that need.